Which word indicates a mandatory action in the Rules of Golf?

The term indicating a mandatory action in the Rules of Golf is "must." This word conveys an obligation or requirement that players are expected to follow without exception. When a rule states that a player "must" perform a certain action, it signifies that adherence to this directive is not optional; compliance is essential to align with the established rules governing play.

In contrast, terms like "should," "may," and "can" introduce flexibility and discretion in decision-making. When a player sees "should," it suggests guidance or recommendation rather than an absolute requirement. "May" indicates permission—the player has the option to act or not. Similarly, "can" implies ability or capability, which does not enforce an obligation to take action.

Understanding these distinctions is crucial for players to navigate the Rules of Golf accurately and to ensure they are abiding by the mandated actions outlined in any situation on the course.